This invention relates to low pressure arc discharge tubes and more particularly to such tubes having an increased voltage drop thereacross.
It is often desirable to have a higher voltage drop across an arc discharge tube. For example, in ballastless discharge lamps it is desirable to raise the voltage across the lamp to equal the line voltage (110 volts in the U.S.; 220 volts in Europe) in order to minimize other circuit losses.
In low power, i.e. 40 W, metal halide discharge lamps it is desirable to operate at about 50 volts across the lamps to maintain stability (approx. 50-60 volts across the ballast). This higher voltage can be obtained by raising the mercury pressure. However, this increases the probability of explosions. Therefore, it is desirable to raise the voltage without increasing the pressure.
It is known in the art that the voltage across an arc discharge tube can be increased by varying the operating parameters of the discharge tube, such as the pressure; the current; the cathode fall; etc. However, altering these parameters effects the performance or some other aspect of the discharge tube.